During the process of providing communication devices such as radios with new encryption information using radio frequency (RF) transmissions ("over-the-air"), messages are sent to individual radios or groups of radios with the new programming information. A typical reprogramming sequence known as "rekeying" provides a radio with new encryption key(s) which the radio can begin to use in order to encrypt/decrypt future communication messages. With a communication key management controller providing new encryption information periodically, the security of communications between communication devices in the system is increased, since it would be futile for an eavesdropper to attempt to decode the encrypted transmissions given the fact that periodically the encryption scheme is changed.
During the process of reprogramming the radios during an encryption rekey sequence, if a radio is turned off, is out of range of the communication system, or is in a condition where the programming information can not reach the radio, that radio(s) would be unable to communicate with the rest of the communication system when the new encryption information goes into effect. Given the complexity of reprogramming radios over-the-air, there is a very good possibility that some number of communication units in the system will lose communications with the system due to some failure in the rekeying process as mentioned before.
Current over-the-air-rekeying (OTAR) systems attempt to compensate for this problem by sending the encryption information on a periodic basis to field units which have not acknowledged the initial rekey command. These re-try attempts are typically sent only a limited number of times and the duration of time between successive retries is usually increased, so that these retries do not increase the loading on the system. Unfortunately, this retry process does not assure that a field unit will be rekeyed promptly when it returns to an active service state (e.g., when it attempts to communicate with another unit). Furthermore, after the key management controller stops the retry process and no more retry attempts are sent, a field unit may have no chance of regaining entry into future encrypted communications.
In present communication system designs, the solution to the previously mentioned rekeying short comings is to increase the number and the frequency of the retries by the key management controller. This however has a negative impact on system capacity and interferes with future rekeying processes (e.g., if some radios have yet to be rekeyed from the previous rekey operation and new rekey sequence is now being sent out). Thus a need exists for a method and apparatus for providing new programming information such as encryption information to communication devices in a more efficient and timely manner.